Hollow Spherical Structure Research Articles

Experimental and numerical studies on compressive mechanical properties of hollow-sphere structures with perforations

The compressive mechanical properties of perforated hollow-sphere structures (PHSSs) are studied through experiments and numerical simulations. In a PHSS, hollow spheres perforated with several holes, which are to open the inner volumes and surface areas of the hollow spheres, are connected in simple cubic (SC), body centered cubic (BCC) or face centered cubic (FCC) pattern. In experiments, the unit cell and multi cell structures in the BCC arrangement are fabricated through 3D printing technology, and the results indicate deformation behaviors similar to those of classic hollow-sphere structures. Then, the effects of geometric properties, such as wall thickness, hole diameter, linking neck radius, and the spatial arrangement of the spheres, on the structural Young's modulus and initial yield stress are calculated and analyzed using the finite element method (FEM). Finally, the relationships between the mechanical properties and relative densities of different sphere arrangements are also obtained by nonlinear fitting.

Polypyrrole-Coated Sodium Manganate Hollow Microspheres as a Superior Cathode for Sodium Ion Batteries.

Advanced electrode materials play a very important role in the development of large-scale production of sodium-ion batteries. Herein, Na0.7MnO2.05 hollow microspheres with diameters of 2 μm and a shell thickness of 200 nm are prepared and then modified by polypyrrole (PPy) coating. As cathodes for sodium-ion batteries, the designed PPy-coated sodium manganate hollow microspheres demonstrate enhanced electrochemical performances, with an initial capacity of 165.1 mAh g-1, capacity retention of 88.6% at 0.1 A g-1 after 100 cycles, and improved rate capability. The excellent electrochemical properties are attributed to the improved electroconductivity and the high stability of hollow spherical structure of sodium manganate oxide particles due to the introduction of conductive polymer coating.

NiCo2S4 yolk-shell hollow spheres with physical and chemical interaction toward polysulfides for advanced lithium-sulfur batteries

Lithium-sulfur (Li-S) battery attracts significant attention as the next-generation battery candidate due to its considerable theoretical energy density. However, the shuttle effect of polysulfides and relatively slow reaction kinetics of sulfur cathode severely hinder the commercial applications of the Li-S battery. Herein, we report NiCo2S4 yolk-shell hollow spheres used as an ideal sulfur host in Li-S battery for the first time. Benefiting from the unique yolk-shell hollow sphere structure and the bimetal sulfide component, the as-synthesized NiCo2S4 yolk-shell hollow spheres cannot only effectively physically absorb the polysulfides but also facilitate the polysulfides conversion. Accordingly, the cathode of S/NiCo2S4 composite with 70 wt% sulfur delivers notable cyclic stability up to 500 cycles at 0.5 C with a capacity decay rate of only 0.074% per cycle. Therefore, this unique NiCo2S4 yolk-shell hollow sphere could be considered an efficient sulfur host material candidate for high-energy density Li-S batteries.

Controllable synthesis and photoelectric properties of interconnected and self-assembled nanocomposite of porous hollow Cu7S4/CuS and nitrogen-doped graphene oxide

In this work, the novel, interconnected and self-assembled nanocomposite of porous hollow Cu7S4/CuS and nitrogen-doped reduced graphene oxide (Cu7S4/CuS@nGO) has been designed and synthesized successfully via a simple solvothermal process. An efficiently synthetic approach to selectively manufacture different morphologies of Cu7S4/CuS has been investigated by only controlling the hydrothermal temperature. The images of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicate the temperature-dependent evolution of structures and morphologies of the samples. Considering the efficient morphology of Cu7S4/CuS(synthesized at 210 °C) with the porous hollow spherical structure, we speculate it should have good photoelectric properties, such as wide UV–vis absorption spectra, and its performance should be enhanced with further treatment like being encapsulated with nitrogen-doped reduced graphene oxide. In order to investigate the photoelectric properties of the Cu7S4/CuS and Cu7S4/CuS@nGO nanocomposites, they have been used as the counter electrodes (CE) in the dye-sensitized solar cells (DSSC). It is demonstrated that the Cu7S4/CuS@nGO nanocomposite not only shows the best photoelectric performance, whose power conversion efficiency is 9.14% (much higher than those of the devices with Pt, Cu7S4/CuS and nGO as CEs), but possesses remarkable electrochemical stability as well.

Synergistic effect of ZnO QDs and Sn4+ ions to control anatase-rutile phase of three-dimensional ordered hollow sphere TiO2 with enhanced photodegradation and hydrogen evolution

A novel three-dimensional ordered hollow spherical Sn4+ doped TiO2 material with ZnO quantum dot sensitization (ZnO QDs@Sn-TiO2) was synthesized by a simple colloidal template method. The characterization results indicate that the crystal phase of the prepared composite could be controlled by modifying the loading of ZnO QDs under the synergistic action of ZnO QDs and Sn4+ while maintaining the favorable three-dimensional ordered hollow sphere structure. Based on diffuse reflectance and fluorescence spectroscopy, ZnO QDs provide multiple migration pathways for photogenerated carriers, effectively inhibiting the recombination of photogenerated electron–hole pairs. And the photocatalytic experiments show that the photocatalyst ZnO QDs@Sn-TiO2 has significantly improved photocatalytic performance than pure TiO2. Simultaneously, the optimized results show that 2.0 ZnO QDs@Sn-TiO2 has the best degradation rate and photocatalytic activity. In summary, this work provides a new approach for the synthesis of multi-morphological mixed phase TiO2 photocatalysts for photocatalytic applications.

MOF-Derived Hybrid Hollow Submicrospheres of Nitrogen-Doped Carbon-Encapsulated Bimetallic Ni-Co-S Nanoparticles for Supercapacitors and Lithium Ion Batteries.

The development of bimetallic transition-metal sulfide and nitrogen-doped carbon composites with unique hollow structure is highly desirable for energy storage applications but is also challenging. In the present work, we demonstrate a facile metal-organic framework engaged strategy for synthesizing bimetallic nickel cobalt sulfide and nitrogen-doped carbon composites with hollow spherical structure (denoted as hollow Ni-Co-S- n/NC composites) and a Ni/Co molar ratio ( n value) that can be easily controlled. When evaluated as electrode materials for both supercapacitors and lithium ion batteries, it is found that the hollow Ni-Co-S-0.5/NC composite with a Ni/Co molar ratio of 0.5 exhibits optimal electrochemical performance. The hollow Ni-Co-S-0.5/NC composite exhibits a high specific capacity of 543.9 C g-1 at 1 A g-1 and maintains a capacity retention of 67.3% when the current density is increased to 20 A g-1. An asymmetric supercapacitor based on the hollow Ni-Co-S-0.5/NC composite is fabricated, which shows good electrochemical performance with a high energy density of 39.6 W h kg-1 at a power density of 808 W kg-1. For lithium storage, the hollow Ni-Co-S-0.5/NC composite manifests a high reversible discharge capacity of 755.0 mA h g-1 at 200 mA g-1 for 200 cycles as well as good rate capability. The excellent electrochemical performance could be attributed to the desirable structural, compositional, and component advantages. This work could offer new insight into the rational design and synthesis of highly efficient electrode materials for both supercapacitors and lithium ion batteries.

Well-defined yttrium phosphate hollow spheres: Synthesis, luminescence, and drug delivery properties

Well-defined yttrium phosphate (YPO4) hollow spheres with controllable structure have been synthesized by a facile template-directed route with 3-aminophenol-formaldehyde (APF) resin as template. The structure, morphology, and formation process of the YPO4 hollow spheres have been investigated in detail. The as-obtained YPO4 hollow spheres inherit the perfect spherical shape and good dispersion of the APF resin template. The ethylene glycol (EG) solvent plays a key role in the morphology of the final YPO4 hollow spheres by impacting the ion exchange process. The Eu3+ and Tb3+ doped YPO4 samples exhibit intense characteristic orange and green emissions under ultraviolet excitation. Moreover, the as-obtained YPO4 hollow spheres show good biocompatibility in terms of in vitro cytotoxicity test and excellent drug loading and sustained drug release behaviors. This synthesis route may be of significance for the design and preparation of other lanthanide functional materials with hollow spherical structure.

Composition-dependent lithium storage performances of SnS/SnO2 heterostructures sandwiching between spherical graphene

Heterostructures have broad potential application in energy conversion material and optoelectronic device since of novel interface effect and enhanced electron transport dynamics at heterointerfaces. Herein, we report a heterostructured SnS/SnO2/spherical graphene composite, in which ultrafine SnS/SnO2 nanoparticles with heterostructures are sandwiched between multi-layers of graphene sheets, exhibiting a hollow spherical architecture as a whole. Detailed electrochemical studies indicate that the molar ratio of SnS to SnO2 has great influence on the charge transport efficiency. Theoretical calculation reveals that SnS and SnO2 exhibit different work functions and the Fermi level shift is affected by the SnS/SnO2 molar ratio, thus the hybrid with the ratio close to 1.0 owns the most adsorbed lithium ions, which leads to the highest specific charge-transfer kinetics and lowest ion-diffusion resistance than other samples. Electrochemical tests show that the composite with appropriate composition delivers the best lithium storage rate performance (620 and 312.7 mAh g−1 at 1 C and 10 C). A much stable and high reversible specific capacity of 850 mAh g−1 is obtained after 200 cycles at 0.1 C. The appropriate molar ratio of nano-heterostructures and the novel sandwich hollow spherical composite structure are attributed to the excellent electrochemical performances.

Enhancing photocatalytic activity of tantalum nitride by rational suppression of bulk, interface and surface charge recombination

Rational design of photocatalysts is essential to achieve efficient solar energy conversion. For narrow bandgap Ta3N5 photocatalyst, various charge recombination occurring in the bulk, interface and on the surface significantly impairs its activity for solar hydrogen (H2) generation. Herein, a synergistic engineering approach is designed to solve this critical recombination challenge. First, hollow spherical structure of Ta3N5 with Mg doping is prepared to not only reduce the charge migration distance and increase the surface area, but also increase the electron mobility for facilitated charge transfer. Second, an MgO nano-layer covers the surface of hollow Ta3N5 structure to passivate surface defects, thus promoting the interfacial charge transfer between Ta3N5 and co-catalysts. Finally, dual co-catalysts (Pt/CoOx) for redox reactions are loaded onto the hollow Ta3N5 structure to reduce the surface recombination and overcome the sluggish surface reaction. Remarkably, the combination of hollow structure, Mg2+ doping, MgO interfacial layer, and dual co-catalysts effectively improves the charge separation and transfer in Ta3N5 photocatalyst. This newly designed photocatalyst exhibits a considerably improved H2 generation performance of 56.3 μmol h−1 under simulated sunlight, compared to that of reference Pt/Ta3N5 hollow spheres.

Designed mesoporous hollow sphere architecture metal (Mn, Co, Ni) silicate: A potential electrode material for flexible all solid-state asymmetric supercapacitor

The high performance of a supercapacitor device relies largely on the nanoarchitectures scrupulous designed and electrode material used. In this work, by utilizing Stöber method-prepared SiO2 sphere as a template, porous hollow spherical nanostructured metal silicates (MnSi, CoSi and NiSi) were synthesized by a hydrothermal method. When MnSi, CoSi and NiSi were used as effective positive materials for asymmetric supercapacitor, they exhibited a battery-type redox behavior and a relatively high charge storage property (517.0, 452.8, 66.7 F g−1 at 0.5 A g−1) in an aqueous alkaline electrolyte. The excellent electrochemical performance is mainly based on the large surface area of metal silicates, and the porous hollow spherical structure facilitates fast electrolyte ions and electrons transportation. More importantly from the practical applications, three high capacity performance, flexible asymmetric solid-state supercapacitor devices were assembled by employing metal silicates as an effective positive electrode and activated carbon as negative material in PVA-KOH gel electrolyte. The MnSi//AC, CoSi//AC and NiSi//AC device showed an areal capacitance of 1048.3, 375.5 and 120.9 F cm−2, corresponding to a high energy density of 4.6, 2.6 and 0.93 mWh cm−3, respectively. The detailed formation mechanism and electrochemical mechanism of metal silicate is performed experimentally and theoretically. The results reveal that MnSi, CoSi and NiSi have a potential application in energy storage.

Synergistic Dual-Confinement Effect: Merit of Hollowly Metallic Co9S8 in Packaging Enhancement of Electrochemical Performance of Li–S Batteries

Lithium–sulfur (Li–S) batteries have become a powerful alternative for lithium-ion batteries due to their high energy density and high specific capacity. However, several problems still hinder its practical application, such as poor electron conductivity, large volumetric expansion, and severe shuttle effect. To overcome these obstacles, a metallic and polar sphere-like Co9S8 with high electron conductivity is designed and prepared. Merited from a large chemical affinity and improved integration with polar polysulfides (LiPSs), Co9S8 enables chemically immobilizing LiPSs effectively with an improved cycle life of Li–S batteries. Besides, the hollow sphere structure can physically block the diffusion of LiPSs into electrolyte. Sufficient internal space can accommodate more active materials and mitigate the volume expansion. The high electron conductivity of Co9S8 facilitates improving of electrochemical reaction kinetics. Thus, serving as host material for Li–S batteries, the Co9S8 electrode exhibits a high initial specific capacity of ∼1200 mAh/g at 0.1 C and the discharge specific capacity retains 570 mAh/g after 100 cycles at 0.5 C.

MOFs-derived magnetic chestnut shell-like hollow sphere NiO/Ni@C composites and their removal performance for arsenic(V)

Well-ordered, hollow, magnetic, high specific surface area composites have recently received enormous attention for the treatment of pollutants containing heavy metal ions. Herein, a serious of magnetic chestnut shell-like hollow sphere structure composites (NiOx/Ni@C) were derived via pyrolyzing a MOF containing nickel as self-sacrificed template and served as adsorbent materials for arsenic(V) (As(V)) removal from aqueous solutions. The experimental results indicated that the adsorption capacity of NiO/Ni@C400 towards As(V) (454.94 mg/g) was higher than that of Ni@C600 (342.77 mg/g), Ni@C500 (290.89 mg/g), NiO@C300 (210.40 mg/g), and Ni-MOFs (133.93 mg/g), which could be ascribed to NiO/Ni@C400-rich oxygen-containing functional groups and high specific surface area. The NiO/Ni@C400 had a high magnetization intensity and could be easily separated under external magnetic field. In addition, the NiO/Ni@C400 had an excellent As(V) removal performance over a broad pH range from 1 to 10. The significant adsorption capacity and reusability of the NiO/Ni@C400 coupled with the easy separation property indicated that the NiO/Ni@C400 has great potential in As(V) purification industry.

A confined space pyrolysis strategy for controlling the structure of hollow mesoporous carbon spheres with high supercapacitor performance.

Hollow mesoporous carbon spheres (HMCSs) have been widely used in energy storage due to their high chemical stability, high surface area, thermal insulation, low effective density and high compressive strength. The electrochemical properties of HMCSs are related to their inner structure. In this work, we demonstrate a facile and controllable synthesis of HMCSs with a tunable inner structure by a confined space pyrolysis strategy. In this process, a phenolic resin oligomer solid sphere is coated with a layer of compact silica. The solid resin sphere can be transformed into a HMCS with a hollow or yolk-shell structure by direct annealing treatment in the silica shell. The compact silica shell can provide a confined space for the pyrolysis of the solid phenolic resin, producing carbon spheres with a hollow cavity, abundant mesopores and a high specific surface area without the use of a template agent. Moreover, the amount of silica precursor and the polymerization time of the resin sphere have great influence on the inner structure of the HMCSs. As an electrode material for supercapacitors, HMCSs display excellent performance with a specific capacitance of 352 F g-1 at a current density of 0.5 A g-1, which is promising for high performance energy storage.

MOF-templated self-polymerization of p-phenylenediamine to a polymer with a hollow box-assembled spherical structure.

This paper presents the first transformation of MOFs to polymers without any additives by using a one-step MOF-templated self-polymerization approach. We investigate the conversion process and demonstrate that the MOF-templated self-polymerization is a new and effective approach for the in situ conversion of organic ligands to polymers and even carbon nanomaterials with maintained MOF configurations.

Self-Templated Formation of Hollow Yolk-Like Spheres Iron Fluoride as Cathode Material for High-Performance Li-Ion Batteries

Iron fluoride is one of the representatives of multi-electron cathode materials for Li-ion batteries, which has attracted extensive attention. However, its poor rate performance and volume adaptability during charge-discharge cycles hinder its practical application. To solve these defects, hollow yolk-like spheres iron fluoride with micro-nano architectures has been synthesized by a new self-templated solvothermal method. Fe-glycerate precursor with hollow yolk-like spheres was first prepared and subsequent performing ion exchange with NH4F as fluorine source to form iron fluoride. The formation mechanism of the hollow yolk-like spheres Fe-glycerate is attributed to “Kirkendall effect”. The hollow yolk-like spheres iron fluoride delivers a superior rate performance of 163 mAh g−1 at high current density of 712 mA g−1, with a low capacity fading rate of 0.58% per cycle for 40 cycles. Moreover, it displays a high discharge capacity of 306 mAh g−1 at 71.2 mA g−1. The superior electrochemical performance is attributed to the large specific surface area, short electrons and ions migration distance and hollow structure for electrolyte penetration deriving from the unique micro-nano hierarchical hollow yolk-like spheres structure. This work provides a new and general method for controllable synthesis of hollow structure materials for high rate performance Li-ion batteries.

Template-directed synthesis, properties, and dual-modal bioapplications of multifunctional GdPO4 hierarchical hollow spheres

Well-defined GdPO4 hierarchical hollow spheres have been synthesized via a novel template-directed synthesis approach with 3-aminophenol-formaldehyde resin spheres as template. The core-shell structured precursor was firstly prepared by a homogeneous precipitation and subsequent hydrothermal route. Finally, the GdPO4 hollow spheres were obtained after an annealing process in air. The phase structure, morphology, and formation process were also investigated in detail. Moreover, the as-synthesized GdPO4 hollow spheres show good biocompatibility and excellent drug loading and sustained drug release ability. Interestingly, the lanthanide activator ions doped GdPO4 hollow spheres exhibit multimodal imaging functionality for combined optical and magnetic resonance imaging (MRI). Due to the well-defined hollow structure, good biocompatibility, luminescence properties, positive magnetic signal-enhancement ability, and drug loading/release patterns, the as-obtained GdPO4 samples may be potentially applied in fields of bioimaging, drug delivery, and disease diagnosis. Furthermore, this novel synthetic strategy may pave a critical way for the preparation of other similar lanthanide orthophosphate functional materials with perfect hollow spherical structure, tunable particle sizes, and good physicochemical properties.

Shrunken hollow Mo-N/Mo-C nanosphere structure for efficient hydrogen evolution in a broad pH range

Finding a non-noble metal (NNM) electrocatalyst with comparative hydrogen evolution reaction (HER) activity in a broad pH range is essential but challenging. Here, we report a unique shrunken hollow spherical shell with Mo2N and Mo2C dual active phases encapsulated by nitrogen-doped carbon (Mo-N/C@N-C). As NNM electrocatalyst, it shows high HER activity and stability in a broad pH range. This material can be synthesized by pyrolysis of sulfonated polystyrene@polyaniline-MoOx sphere-like precursors using sulfonated polystyrene as template and polyaniline as carbon and nitrogen source. In an alkaline solution, the as-prepared Mo-N/C@N-C only needs an overpotential of 135 mV to reach the current density of 10 mA cm−2, and exhibits high electrochemical and structural durability. The catalyst also possesses similar performance in acidic and neutral media, making it a suitable candidate for hydrogen production in all pH media. Such excellent catalytic performance is mainly driven by the synergy of abundant Mo2N and Mo2C dual active centers, and shrunken hollow sphere structures with high packing density, as well as the N-C active site and protection of N-doped carbon frameworks.

Nitrogen-Enriched Hollow Carbon Spheres Coupled with Efficient Co–Nx–C Species as Cathode Catalysts for Triiodide Reduction in Dye-Sensitized Solar Cells

Hollow carbon spheres (hCSs) have recently been emerging as low-cost and promising cathode catalysts toward triiodide reduction for dye-sensitized solar cells (DSSCs). However, it is still challenging and questionable for hCSs-based counter electrodes (CEs) to compete with traditional Pt CEs in DSSCs. Herein, nitrogen-enriched hCSs with atomically dispersed Co–Nx–C moieties (Co–N–hCSs) are synthesized via a calcination of cobalt-ions-absorbed N-enriched hollow copolymer sphere precursor. As inferred from cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel polarization curves, the Co–N–hCSs display superior electrocatalytic activity and electrochemical stability. This excellent catalytic behavior can essentially be attributed to the high intrinsic electrocatalytic activity derived from the Co–Nx–C moieties, along with the robust N-enriched hollow sphere structure. As a result, the DSSCs with Co–N–hCSs as counter electrodes present an encouraging power conversion efficiency of 7.71%, which...

A virtual laboratory for learning fullerene production and nanostructure analysis

AbstractNanotechnology is an emerging technology and it brings a tremendous change to human life and economy. When the size of a material is reduced to the nanoscale, its properties may change significantly and becomes a new substance. A fullerene is a molecule of carbon in the shape of a hollow sphere, ellipsoid, tube, and many other geometrical structures. For example, buckyballs are spherical fullerenes and carbon nanotubes are cylindrical fullerenes. Fullerenes have been under intensive investigation for their expanding applications in electronics, energy, medicine, and many other research fields. Nanostructure analysis is very important for understanding the formation of different materials and their properties. In this study, a virtual laboratory is developed for learning fullerene production and its nanostructure analysis. The learners can use the arc discharge equipment to produce fullerenes and then use the transmission electron microscope (TEM) to observe the nanostructures of different fullerene samples. The high interactivity and 3D visual effects of the virtual laboratory enable the learners to become familiar with the geometrical structures and properties of fullerenes. A teaching experiment has been conducted and the results show that the virtual laboratory can improve their learning motivation and effectiveness.

Copper-cobalt Bimetallic Oxides-doped Alumina Hollow Spheres: A Highly Efficient Catalyst for Epoxidation of Styrene

Copper-cobalt bimetallic oxides-doped alumina hollow spheres(CuCo/AHS) were fabricated through the sacrificial carbonaceous template strategy. The dependence of the physicochemical properties and morphologies of CuCo/AHS on the composition of copper and cobalt in CuxCoy/AHS(x/y=9/1, 7/3, 5/5, and 3/7) were characterized by X-ray powder diffraction, nitrogen physisorption, atomic adsorption spectroscopy, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Among these catalysts, Cu7Co3/AHS catalyst exhibited perfect hollow sphere structure, thin wall, and big pore size. The calcined catalysts were examined for the epoxidation of styrene with tert-butyl hydroperoxide as oxidant. Compared with the monometallic counter-parts(Cu/AHS and Co/AHS) and other CuxCoy/AHS catalysts, Cu7Co3/AHS catalyst showed higher performance, yielding a styrene conversion of 64.6% with 93.0% selectivity toward styrene oxide. In addition, the strong interaction of Cu2+ or Co2+ with AHS ensured the good stability after four consecutive reactions.